I am guessing on this one, but I would say from any distance they would sound similar in intensity of sound (a mortar and gun of comparable size) Close up, I might say the mortar would be louder. It is the same effect with firearms, a short-barreled handgun will sound louder to the one discharching it than a long barreled handgun (of the same caliber). From a distance, however, this effect is not as pronounced, and have heard many say it is actually reversed. I cannot claim this as fact, as I have not done any type of study on it, but I do know it holds true in terms of the comparative loudness with regards to the individual discharging the weapon.